1. Field of the Invention
The invention pertains generally to wireless ad-hoc networking, and more particularly to a medium access control protocol that provides correct collision-avoidance in wireless networks in which hidden terminals may exist.
2. Description of the Background Art
As the use of wireless systems become increasingly important, attention is being focused on a variety of wireless network protocols. A large body of work exists on the design of medium access control (MAC) protocols for wireless networks having hidden terminals. A number of problems have been identified with existing and proposed wireless protocols. One problems is the hidden-terminal problem of carrier sensing which reduces the performance of the carrier-sense multiple access (CSMA) protocol to that of the pure ALOHA protocol when the senders of packets are unable to hear one another, wherein the vulnerability period of packets extends to twice a packet length. The BTMA (busy tone multiple access) protocol was an early attempt to solve the hidden-terminal problem by introducing a separate busy tone channel. In addition, SRMA (split-channel reservation multiple access) was proposed for avoiding collisions by introducing a control-signal handshake between the sender and the receiver. A station in need of transmitting data to a receiver is thereby required to first send a request-to-send (RTS) signal packet to the receiver, wherein the receiver should respond by sending a clear-to-send (CTS) signal if it receives the RTS correctly. Therefore, a sender transmits a data packet only after successful receipt of a CTS. ALOHA and CSMA can be utilized by senders to transmit RTS signal packets.
A number of variations of SRMA have been proposed, and or developed, including MACA, MACAW, IEEE 802.11, FAMA, and so forth. These example protocols and the majority of protocols which are based on collision-avoidance handshakes are designed as sender-initiated protocols in which the node that wants to send a data packet must first gain permission from the receiver by transmitting an RTS and receiving a CTS. In contrast, when utilizing the MACA by invitation (MACA-BI) protocol the receiver polls one of its neighbors asking if it has a packet to send. A reduction in control traffic is an attractive theoretical benefit that could be derived from the use of a receiver-initiated protocol. However, the MACA-BI protocol when utilized in a wireless network is unable to prevent data packet collisions within networks containing hidden terminals.
It will be appreciated, therefore, that a need exists for a wireless protocol that is capable of garnering the benefits of a receiver-initiated protocol while avoiding packet collision within networks which contain hidden terminals. The present invention satisfies those needs, as well as others, and overcomes the deficiencies of previously developed wireless network protocols.